How hard do Great White sharks bite?
By Jonah Fisher
BBC News, Mossel Bay
One foot dangling in the water, marine biologist Enrico Gennari calls out to the shark circling the boat.
"Come on, Come on, you can do it," he says, as the three-metre Great White cruises to within a few centimetres of the bait before turning disdainfully away.
This was not how I had imagined an experiment into a shark's biting strength would be.
Enrico had spent the previous three hours hanging what he calls "The Bitemeter" in the water. But the long metal rod with a bag of fishy remains at the end of it was not having much success.
The problem was not attracting the sharks. The volunteers who help with the research had deposited vast amounts of fish-flavoured water around our boat and we had a steady stream of visitors.
It was just that they did not really seem in the mood to eat.
"Look at the marks on the gill. It's Roxanne," Enrico declared proudly as he recognised a passing shark. "We've know her for quite a while, We've tagged her a few months ago and tracked her."
Way of life
But Roxanne like the other sharks was interested in circling the boat but not in tasting "The Bitemeter".
Enrico and the three volunteers had to be satisfied with photographing fins and occasionally plunging a pole into the shark's side to get a DNA sample.
It all forms part of research being conducted by the South African Marine Predator Laboratory (Sampla) in Mossel Bay.
Its aim is to build up a complete picture of the Great White's way of life.
"Humans can take the attitude: Let's just kill all the sharks and we can be safe," Ryan Johnson, another of Sampla's scientists, told me.
"Or you can try and understand them and work out where they are at certain places in the bay and with that type of knowledge mitigate the threat they pose to us."
As well as being home for about 80 Great Whites, Mossel Bay is also a popular tourist destination.
Thanks in part to information that Sampla has provided, there has not been a fatal attack for almost 20 years.
In many parts of South Africa and Australia surfers sometimes get mistaken for the Great White's favourite food - seal.
But in Mossel Bay the surfers have been told where is safe and at what time of day.
"There are quite a few [sharks] but we haven't had problems here," one surfer told me as he emerged unscathed from the waves.
"If you go round the point there, there's a couple more sharks closer to the seals."
After three-and-a-half hours a shark nipped "The Bitemeter"
In Mossel Bay's tourism office, brochures for shark cage diving sit alongside those for beach resorts.
"The people are quite safe. The sharks stay around the island," Marcia Holm, the operations manager, says.
"The island has lots of seals and that's their diet - they don't really like humans."
After three-and-a-half hours on the water a shark puts Enrico out of his misery - and gives "The Bitemeter" a nip.
"It was just 89 pounds per square inch - just a little bit more than a human bite," he announces triumphantly.
But for Enrico, a day spent trying to get a Great White to bite also proves that they are not demonic creatures attacking everything in sight.
"This shows us that the Great Whites aren't animals that bite something every time they meet it.
"It's not an incredible Pac-Man that bites everything. It's a very cautious animal."